1. Field of the Invention
The present invention relates to a lens assembly, and more particularly to a three-piece lens assembly.
2. Description of the Prior Art
Along with the miniaturization of the digital camera and the mobile phone, the lens assembly used in the digital camera and the mobile phone also has a tendency toward miniaturization, therefore, the imaging device usually takes the form of CCD sensor (charge coupled device) or CMOS sensor (Complementary Metal Oxide Semiconductor). However, along with the miniaturization of the imaging device, the resultant optical length is also shortened. Therefore, the design of incident angle becomes particularly important.
In the past, a plastic-made triplet aspheric lens with point of inflexion was developed to achieve miniaturization and to improve the incident angle, thus F ensuring the optical performance of the lens and the accomplishment of designing a precision incident angle, and effectively shortening the optical length.
Please refer to the three patent documents, 1: JP Pt. No. 2005-173298, 2: JP Pt. No. 2005-242286, and 3: JP Pt. No. 2005-309210.
The optical lens assembly in Document 1, starting from the object side, comprises a first lens group, an aperture, a second lens group and a third lens group. The first lens group includes a positive meniscus lens whose convex surface faces the object side, the second lens group includes a meniscus lens with a convex surface facing the image side, and the second lens group includes a negative lens (in the embodiment, the negative lens is a meniscus lens with a convex surface facing the object side).
The optical lens assembly in Document 2 also comprises three lenses and an aperture that are arranged similarly to the Document 1, the first lens group includes a positive lens with a convex surface facing the object side, the second lens group includes a positive lens (which is a positive meniscus lens in the embodiment) with a convex surface facing the image side, and the third lens group includes a negative lens (which is a negative meniscus lens in the embodiment) with a concave surface facing the image side.
The optical lens assembly in Document 3 also comprises three lenses and an aperture that are arranged similarly to the Document 1, wherein the first lens group includes a positive lens with a convex surface facing the object side, the second lens group includes a meniscus lens with a concave surface facing the object side, and the third lens group has a function of aberration compensation. In the embodiment, the first lens group is a positive meniscus lens or a biconvex lens, the second lens group is a positive or negative meniscus lens, and the third lens is a negative meniscus lens or a biconcave lens.
However, the abovementioned three optical lens assemblies disclosed in the three documents still have many problems. For example, the magnification of the Document 1 is relatively great, approximately 1.35-1.43, and the magnification of the Document 1 is also great, approximately 1.35-1.48. The magnification of the Document 3 is relatively small, approximately 1.18-1.20, however, the resultant angle of view is as low as 62°, which results in some problems. (magnification T/f is the proportion between the total focal length f of the whole optical system and the entire optical length T).
In view of the abovementioned problems, in the optical technology field, it needs a three-piece imaging taking lens assembly that not only has a miniaturized size but also has a wide angle of view and a good performance of aberration compensation.